The present invention relates to a wire saw used to cut an ingot-shape work of brittle material such as semiconductor material, magnetic material, ceramic, etc. simultaneously into a plural of sheets each having a prescribed thickness, and a work slicing method using it.
In a previously known wire saw of this kind, plural rollers for machining are arranged in parallel at prescribed intervals, and on the outer periphery thereof, plural strips of circular grooves are arranged with a prescribed pitch. A supply reel and a take-up reel in a pair, separated from the above machining rollers, are arranged oppositely to each other. A strip of wire supplied from the supply reel is wound on the circular grooves of each roller and travelled among these rollers. Thereafter, it is wound by the take-up reel. A slurry containing free abrasive grains is supplied to the wire travelling among the plural machining rollers so that the work is sliced into wafers each having a prescribed thickness by the lapping operation of the abrasive grains. Thus, the wafers are cut out.
In the above conventional wire saw, however, a strip of wire is continuously wound from the circular groove at the one end to that at the other end on the outer periphery of each machining roller. Therefore, the wire is shifted successively from the circular groove at the one end of the roller to that at the other end thereof in accordance with the rotation of the machining roller. Then, the wire is gradually abraded to become thin so that the thickness of the sliced work varies between the inlet side of the machining roller and the outlet side thereof.
When the wire becomes gradually slender during the shift of the wire from the one end of the roller to the other end thereof, the application degree of free abrasive grains for the wire is reduced. Thus, the cutting capability is gradually reduced from the one end of the machining roller to the other end thereof. The cutting plane of the work becomes gradually coarse.
The slicing speed of the work inclusive of the travelling speed of the wire must be set in accordance with the low cutting capability of the wire at the other end of the roller. Therefore, the slicing speed of the work cannot be accelerated so that it takes a long time to cut/slice the entire work.
In addition, in a wire saw developed recently, in order that a large number of wafer sheets are cut out simultaneously, the wire is likely to be thick and long. For the machining of the long work, the length of the machining roller in an axial length must be large to increase the number of the circular grooves. In this case, a single wire cuts out a large number of wafers so that the abrasion degree of the wire is further increased. Thus, the variation in the cutting thickness of the work, cutting capability and coarseness of the cutting plane becomes worse remarkably between the one end of the roller and the other end thereof.
Further, since the wire saw developed in recent years is required to cut a long work into many wafers simultaneously, the machining roller having longer lengths in the axial direction have been employed. However, if the machining roller becomes too long, when the work is cut/sliced, it becomes hot due to friction between the machining roller and wire. This may provide great thermal distortion in the roller, and a large fluctuation in the pitch of the circular grooves. The work cannot be cut into wafers each having a prescribed thickness with a high precision.